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Showing content from https://docs.microsoft.com/en-us/dotnet/api/system.data.uniqueconstraint below:

UniqueConstraint Class (System.Data) | Microsoft Learn

UniqueConstraint Class Definition

Represents a restriction on a set of columns in which all values must be unique.

public ref class UniqueConstraint : System::Data::Constraint

public class UniqueConstraint : System.Data.Constraint

[System.Serializable]
public class UniqueConstraint : System.Data.Constraint

type UniqueConstraint = class
    inherit Constraint

[<System.Serializable>]
type UniqueConstraint = class
    inherit Constraint

Public Class UniqueConstraint
Inherits Constraint

Inheritance

Attributes

Examples

The following example adds a UniqueConstraint to a DataSet and sets the EnforceConstraints property to true.

Public Sub CreateDataTable()
    Dim dataTable As New DataTable()
    dataTable.Columns.Add("CustomerID", Type.GetType("System.String"))
    dataTable.Columns.Add("CompanyName", Type.GetType("System.String"))

    Dim uniqueConstraint As UniqueConstraint = _
      New UniqueConstraint("CustConstraint", _
      New DataColumn() {dataTable.Columns("CustomerID"), _
      dataTable.Columns("CompanyName")})

    dataTable.Constraints.Add(uniqueConstraint)
End Sub

The UniqueConstraint is enforced on a single column (or columns) to ensure that a primary key value is unique.

Constraints are not enforced unless the EnforceConstraints property is set to true.

When the a DataSet is merged with a second DataSet, constraints are not enforced until all merges are completed.

Constructors UniqueConstraint(DataColumn, Boolean)

Initializes a new instance of the UniqueConstraint class with the DataColumn to constrain, and a value specifying whether the constraint is a primary key.

UniqueConstraint(DataColumn)

Initializes a new instance of the UniqueConstraint class with the specified DataColumn.

UniqueConstraint(DataColumn[], Boolean)

Initializes a new instance of the UniqueConstraint class with an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key.

UniqueConstraint(DataColumn[])

Initializes a new instance of the UniqueConstraint class with the given array of DataColumn objects.

UniqueConstraint(String, DataColumn, Boolean)

Initializes a new instance of the UniqueConstraint class with the specified name, the DataColumn to constrain, and a value specifying whether the constraint is a primary key.

UniqueConstraint(String, DataColumn)

Initializes a new instance of the UniqueConstraint class with the specified name and DataColumn.

UniqueConstraint(String, DataColumn[], Boolean)

Initializes a new instance of the UniqueConstraint class with the specified name, an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key.

UniqueConstraint(String, DataColumn[])

Initializes a new instance of the UniqueConstraint class with the specified name and array of DataColumn objects.

UniqueConstraint(String, String[], Boolean)

Initializes a new instance of the UniqueConstraint class with the specified name, an array of DataColumn objects to constrain, and a value specifying whether the constraint is a primary key.

Properties Methods Thread Safety

This type is suitable for multithreaded read operations. You must synchronize any write operations.